The purpose of this investigation is to accumulate data relative to gait or other appropriate activities in abnormal conditions of the hip and to study the mechanical basis of these disorders and their treatment. Engineering knowledge in the field of statics, kinematics and dynamics will be used to develop an understanding of the pathophysiology of hip disease such as osteoarthritis, rheumatoid fractures and other conditions. This information will be utilized in the development of improved methods of treatment of hip disorders. The results of treatment will be further modified in a continuing study. The second purpose of this investigation is to refine our present method of study to improve the efficiency in obtaining data from patients and improve the accuracy of our results.